Organic coatings offer the most common and cost-effective protection for metallic structures against degradation in corrosive environments. However, the metal substrate loses this passive protection when disruption of the coating occurs. Recently, active corrosion protection coatings, commonly referred to as “smart coating, intelligent coating, functional coating, or self-healing coating,” have become an attractive research topic. A smart coating is a coating with incorporated “smart” micro/nanostructured containers or carriers. These containers filled with corrosion inhibitors not only preferably preclude the direct contact between the active anticorrosive agent and the adjacent environment (such as paint resins), but, intelligently release the host active agent at a corrosion site over a period of time. Such a coating with dispersed “smart containers” can provide long-term effective corrosion protection for metallic substrates. For example, U.S. Pat. No. 7,790,225 discloses a coating with pH-sensitive microcapsules that contain and release anticorrosive agents. A change of pH induced by the metallic corrosion process can be used as a trigger to break down or disintegrate the shells chemically to release the active compounds on-site.
Many organic and inorganic anticorrosive compounds can be encapsulated in polymeric carriers, but some highly reactive and very water-soluble agents (mostly ionic compounds) are difficult to incorporate in organic matrices. Polymeric microcapsules, prepared by water-in-oil micro-emulsion polymerization, for example U.S. Pat. No. 9,227,221, were designed for encapsulation of water-soluble inorganic corrosion inhibitors. However, some water-soluble corrosion inhibitors cannot be encapsulated by these polymer capsules due to the reactivity of the inhibitors in the presence of the carrier materials.
New controlled-release anticorrosion materials are needed, particularly for controlled-release of water-soluble anticorrosion agents.